Correct some apparent misspellings of BB_NUMBER_THREADS. (Bitbake rev: 175e55db8f0762a2f2f0aaf3ca48169016b9ef6b) Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>