iio:common: added allocate and deallocate trigger functions when trigger is disabled.
iio:common: added allocate and deallocate trigger functions when trigger is disabled.

This patch resolve a bugfix when driver is compiled without trigger.

Signed-off-by: Denis Ciocca <4a3a1b0e59e4bf62df5d92c6ace86f220d56cdac@st.com>
Reported-by: Randy Dunlap  <6f29df8e90a57f1ba61ffd63b0468c86bb6d3a99@infradead.org>
Signed-off-by: Jonathan Cameron <09f65b71b7655725897b2fd41a09a0cefe2e1ace@kernel.org>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs