coding guidelines: comply with MISRA C:2012 Rule 4.1

MISRA C:2012 Rule 4.1 (Octal and hexadecimal escape sequences shall be
terminated.)

Use string literal concatenation to properly terminate hexadecimal
escape sequences.

Signed-off-by: Abramo Bagnara <abramo.bagnara@bugseng.com>
Signed-off-by: Simon Hein <SHein@baumer.com>