Staging: Gasket: shift wrapping bug in gasket_read_modify_write_64()

This function only has one caller so mask_width is 1 and mask_shift is
32.  Shifting an int by 32 bits is undefined, but I guess on GCC it
wraps to 0x1?  Anyway it's supposed to be 0x100000000.

Fixes: 9a69f508 ("drivers/staging: Gasket driver framework + Apex driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>