[NFC] fix trivial typos in documents and comments

"is is" -> "is", "if if" -> "if", "or or" -> "or"

llvm-svn: 329878
diff --git a/llvm/docs/AMDGPUUsage.rst b/llvm/docs/AMDGPUUsage.rst
index c07df67..d6255c8 100644
--- a/llvm/docs/AMDGPUUsage.rst
+++ b/llvm/docs/AMDGPUUsage.rst
@@ -2269,7 +2269,7 @@
                 > 1)                              wavefront lane.
      ========== ========================== ====== ==============================
 
-The setting of registers is is done by GPU CP/ADC/SPI hardware as follows:
+The setting of registers is done by GPU CP/ADC/SPI hardware as follows:
 
 1. SGPRs before the Work-Group Ids are set by CP using the 16 User Data
    registers.