staging: mt7621-mmc: Fix unmatched release_mem_regin

Current code calls release_mem_regin on driver remove without
requesting it explicit first. The region is only requested via
devm_ioremap_resource and that releases it automatically. Removing the
release_mem_region calls fixes this.

Signed-off-by: Christian Lütke-Stetzkamp <christian@lkamp.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>