target/arm: Fix return values in fp_sysreg_checks()

target/arm: Fix return values in fp_sysreg_checks()

The fp_sysreg_checks() function is supposed to be returning an
FPSysRegCheckResult, which is an enum with three possible values.
However, three places in the function "return false" (a hangover from
a previous iteration of the design where the function just returned a
bool).  Make these return FPSysRegCheckFailed instead (for no
functional change, since both false and FPSysRegCheckFailed are
zero).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210520152840.24453-6-peter.maydell@linaro.org