Fix default setting for ew_step and ns_step parameter

Fix default setting for ew_step and ns_step parameter which must be "none" rather than 1.5 (which leads to wrong default values in GRASS GIS)

python/plugins/processing/algs/grass7/description/r.resamp.bspline.txt

@@ -4,8 +4,8 @@ Raster (r.*)
 QgsProcessingParameterRasterLayer|input|Input raster layer|None|False
 QgsProcessingParameterRasterLayer|mask|Name of raster map to use for masking. Only cells that are not NULL and not zero are interpolated|None|True
 QgsProcessingParameterEnum|method|Sampling interpolation method|bilinear;bicubic|False|1|False
-QgsProcessingParameterNumber|ew_step|Length (float) of each spline step in the east-west direction|QgsProcessingParameterNumber.Double|1.5|True|0.0|None
-QgsProcessingParameterNumber|ns_step|Length (float) of each spline step in the north-south direction|QgsProcessingParameterNumber.Double|1.5|True|0.0|None
+QgsProcessingParameterNumber|ew_step|Length (float) of each spline step in the east-west direction|QgsProcessingParameterNumber.Double|None|True|0.0|None
+QgsProcessingParameterNumber|ns_step|Length (float) of each spline step in the north-south direction|QgsProcessingParameterNumber.Double|None|True|0.0|None
 QgsProcessingParameterNumber|lambda|Tykhonov regularization parameter (affects smoothing)|QgsProcessingParameterNumber.Double|0.01|True|0.0|None
 QgsProcessingParameterNumber|memory|Maximum memory to be used (in MB). Cache size for raster rows|QgsProcessingParameterNumber.Integer|300|True|10|None
 *QgsProcessingParameterBoolean|-n|Only interpolate null cells in input raster map|False|True