dmaengine: shdmac: avoid unused variable warnings

This driver uses '#ifdef CONFIG_ARCH_SHMOBILE' and '#ifdef CONFIG_ARM'
interchangeably in its sh_dmae_probe function, which causes a build
warning when building for ARM without also enabling shmobile:

dma/sh/shdmac.c: In function sh_dmae_probe:
dma/sh/shdmac.c:696:6: warning: unused variable errirq [-Wunused-variable]
dma/sh/shdmac.c:695:16: warning: unused variable irqflags [-Wunused-variable]
dma/sh/shdmac.c: At top level:
dma/sh/shdmac.c:447:20: warning: sh_dmae_err defined but not used [-Wunused-function]

This changes all the #ifdef to test for CONFIG_ARCH_SHMOBILE to
avoid that warning. An earlier patch from Laurent had fixed the warning
for non-ARM case, but it still remained present in ARM randconfig builds.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 52d6a5ee ("DMA: shdma: Fix warnings due to declared but unused symbols")
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>