ASoC: omap-mcbsp: Fix use of uninitialised pointer

ASoC: omap-mcbsp: Fix use of uninitialised pointer

Commit 2b1729a51989 ("ASoC: omap-mcbsp: Re-arrange files for core McBSP
and Sidetone function split"), in rearranging various files, also replaced
calls to platform_get_resource_by_name() + devm_ioremap_resource() with a
single call to devm_platform_ioremap_resource_byname(). However, the
struct resource is needed as we access its members so at present a null
pointer is dereferenced. Fix by doing things the old way.

Fixes: 2b1729a51989 ("ASoC: omap-mcbsp: Re-arrange files for core McBSP and Sidetone function split")
Signed-off-by: Alex Dewar <alex.dewar90@gmail.com>
Link: https://lore.kernel.org/r/20201004102535.325547-1-alex.dewar90@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>