of: slimbus: Avoid memory leak of boardinfo array

boardinfo structure array populates slaves on the slimbus.
Framework populates devices specified by the boardinfo array and
the array is not referenced later. Also, while reallocating the
array to populate slaves in the loop, make sure that the existing
array is not leaked if reallocation fails during new slave addition.

Change-Id: Ib7e289ee56c57cad2962529270d55bf4107961df
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>