floppy: replace wrong kmalloc(GFP_USER) with GFP_KERNEL

The raw_cmd_copyin() function does a kmalloc() with GFP_USER, although the
allocated structure is obviously not mapped to userspace, just copied from/to.
In this case GFP_KERNEL is more appropriate, so let's use it, although in the
current implementation this does not manifest as any error.

Reported-by: Matthew Wilcox <mawilcox@linuxonhyperv.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>