auxiliary/os: fix the android build - s/drm_munmap/os_munmap/

Squash this silly typo introduced with commit c63eb5dd5ec(auxiliary/os: get
the mmap/munmap wrappers working with android)

Cc: "10.4 10.5" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/gallium/auxiliary/os/os_mman.h

@@ -70,8 +70,8 @@ static INLINE void *os_mmap(void *addr, size_t length, int prot, int flags,
    return __mmap2(addr, length, prot, flags, fd, (size_t) (offset >> 12));
 }
 
-#  define drm_munmap(addr, length) \
-              munmap(addr, length)
+#  define os_munmap(addr, length) \
+             munmap(addr, length)
 
 #else
 /* assume large file support exists */