fault-injection: handle EI_ETYPE_TRUE

Commit af3b8544

 ("mm/page_alloc.c: allow error injection")
introduced EI_ETYPE_TRUE, but did not extend

 * lib/error-inject.c:error_type_string(), and
 * kernel/fail_function.c:adjust_error_retval()

to accommodate for this change.

Handle EI_ETYPE_TRUE in both functions appropriately by
 * returning "TRUE" in error_type_string(),
 * adjusting the return value to true (1) in adjust_error_retval().

Furthermore, simplify the logic of handling EI_ETYPE_NULL in
adjust_error_retval().

Link: https://lkml.kernel.org/r/njB1czX0ZgWPR9h61euHIBb5bEyePw9D4D2m3i5lc9Cl96P8Q1308dTcmsEZW7Vtz3Ifz4do-rOtSfuFTyGoEDYokkK2aUqBePVptzZEWfU=@protonmail.com
Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>