docs: Fix a spelling error in ioctl-number.txt

This commit fixes a misspelled header name in the ioctl numbers list
Signed-off-by: NStan Drozd <drozdziak1@gmail.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/ioctl/ioctl-number.txt

@@ -212,7 +212,7 @@ Code  Seq#(hex)	Include File		Comments
 'c'	00-1F	linux/chio.h		conflict!
 'c'	80-9F	arch/s390/include/asm/chsc.h	conflict!
 'c'	A0-AF   arch/x86/include/asm/msr.h	conflict!
-'d'	00-FF	linux/char/drm/drm/h	conflict!
+'d'	00-FF	linux/char/drm/drm.h	conflict!
 'd'	02-40	pcmcia/ds.h		conflict!
 'd'	F0-FF	linux/digi1.h
 'e'	all	linux/digi1.h		conflict!