debugfs: Fix warnings when building documentation

debugfs: Fix warnings when building documentation

Fix the following warnings:

fs/debugfs/inode.c:423: WARNING: Inline literal start-string without end-string.
fs/debugfs/inode.c:502: WARNING: Inline literal start-string without end-string.
fs/debugfs/inode.c:534: WARNING: Inline literal start-string without end-string.
fs/debugfs/inode.c:627: WARNING: Inline literal start-string without end-string.
fs/debugfs/file.c:496: WARNING: Inline literal start-string without end-string.
fs/debugfs/file.c:502: WARNING: Inline literal start-string without end-string.
fs/debugfs/file.c:581: WARNING: Inline literal start-string without end-string.
fs/debugfs/file.c:587: WARNING: Inline literal start-string without end-string.
fs/debugfs/file.c:846: WARNING: Inline literal start-string without end-string.
fs/debugfs/file.c:852: WARNING: Inline literal start-string without end-string.
fs/debugfs/file.c:899: WARNING: Inline literal start-string without end-string.
fs/debugfs/file.c:905: WARNING: Inline literal start-string without end-string.
fs/debugfs/file.c:1091: WARNING: Inline literal start-string without end-string.
fs/debugfs/file.c:1097: WARNING: Inline literal start-string without end-string

By replacing %ERR_PTR with ERR_PTR.

Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
Link: https://lore.kernel.org/r/20191227010035.854913-1-dwlsalmeida@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>