spi: Replace memset() with __GFP_ZERO

krealloc() as any other kernel memory allocation calls accepts GFP flags,
one of which is __GFP_ZERO. Hence, no need to call memset() explicitly on
the reallocated buffer.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20211122171721.61553-2-andriy.shevchenko@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>