fbdev/g364fb: fix build failure with mips

Fix the typo which resulted in the driver using FB_DEFAULT_IOMEM_HELPERS
instead of FB_DEFAULT_IOMEM_OPS as the fbdev I/O helpers.

Fixes: 50112608

 ("fbdev/g364fb: Use fbdev I/O helpers")
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>